This invention relates to resistance welding and, more particularly, to that area of the art wherein two work-contacting electrodes are utilized, including such various forms as spot welding, seam, stitch and roller welding, and projection welding.
In resistance welding generally, the faying surfaces of the electrically conducting members to be joined are superimposed under pressure. The fusion or coalescence of these surfaces is accomplished by flowing an electric current through a circuit of which the work is a part. In the form of resistance welding of specific concern herein, electrical contact with the work is made, and the loading thereof is typically provided, by means of two opposed electrodes.
As is well appreciated in the art, substantial problems are often encountered on account of surface contamination of the work. Such is especially the case where the work is of an aluminous material, the same typically being quite prone to oxidation on exposure.
Where the outer exposed surfaces of the work are oxidized or otherwise contaminated, the number of acceptable welds obtainable between electrode dressing or replacement can be expected to decrease considerably. Consequently, much attention has heretofore been directed toward providing a cleaning of the work prior to welding.
One such effort is set forth in U.S. Pat. No. 3,278,720 to C. R. Dixon, the disclosure of which is herein incorporated by reference. In accordance with the teaching therein, the work is cleaned by an electric arc shielded by an inert gas. The arc is induced across desired points on the surface of the work and a cleaning head which is positioned in spaced proximity thereto. Welding is then effected in the conventional manner using structurally independent apparatus.
While the electrical cleaning of the work, as described above, has been determined to have a most beneficial result in terms of prolonging electrode life, it has now been discovered that this result can be even further enhanced by also providing an electrical cleaning of the electrodes. That this improvement should obtain is not wholly without explanation, however.
For example, it is reasoned with some logic that a contamination of the electrode working surfaces ought to be equally as disadvantageous as a contamination of the work. Insofar as the electrodes may become generally contaminated in the course of normal operations, it would therefore appear to be of benefit to provide for their cleaning as well.
A more specific way in which electrodes may become contaminated is by oxidation, which is believed to occur under certain conditions. To explain without wishing to become bound thereby, it is believed that such oxidation may be promoted by the phenomenon wherein material from the work becomes plated on, or even alloyed with, the material of the electrodes. It will be appreciated by those who have noticed that this phenomenon to some extent seems to persist regardless of whether the work has been cleaned. So it is theorized that where the work is particularly susceptible to oxidation, such as where it is of an aluminous material, on being sufficiently plated or alloyed the electrode working surfaces ought to become nearly of the same inclination.
Accordingly, it is one object of this invention to provide for an electrical cleaning of the electrodes as well as the work between successive welding operations.
It is another object of this invention to provide for an electrical cleaning of the electrodes as well as the work without the need for a cleaning head which is structurally separate and apart from the electrodes.
Still another object of this invention is to provide an improved apparatus and method particularly adapted for the resistance welding of aluminous materials.
Other objects, uses and advantages of this invention will become readily apparent from an understanding of the exemplary embodiments thereof as presented in the drawings, specification and claims.